The invention relates generally to a drive system and, more particularly, to a flat plate drive for controlling the axial rotational motion of a drive shaft for raising and lowering a load, that optimizes frictional engagement while maximizing heat dissipation away from the moving parts of the drive system. The drive system can be generally used for raising and lowering many types of heavy loads, and is particularly suited for loads that are supported by one or more cables attached to the drive shaft, with the cable extending through a cradle beam which supports a heavy object, such as a boat.
In normal operation, drive systems for lifting boats are usually attached to pilings. The drive system is connected to a drive shaft which runs between the pilings. The cables are attached to the drive shaft, extend through a cradle beam which supports the load, such as the hull of the boat, and are connected on the other end to the lift frame. The drive system allows for the drive shaft to be rotated in either a clockwise or counterclockwise position so as to be able to raise or lower the load.
Existing flat plate drives use an electric motor with a drive belt. The drive belt usually drives a pulley mounted on a thin shaft which carries a worm. The worm drives a toothed cast steel worm gear wheel, which in turn drives a drive shaft. These components are mounted on a backplate which is bolted into place to counteract the torque action of the drive. The load is raised, lowered and held in place by the frictional contact of the worm against the worm gear wheel and the worm bearings. This frictional contact between the worm and the worm gear wheel and the worm bearings causes excessive heat to build up in this area, which increases the temperature. This increase in temperature can cause the worm, worm gear wheel and bearings to wear excessively and to warp and bend as well.
Other drive manufacturers have attempted to solve the problem of excessive heat buildup and gear wear by using anti-friction thrust bearings at the worm and using lubricants retained at the worm. However, the heat buildup often causes the lubricant to break down and no longer be effective. Others have experimented with the use of high temperature lubricants. However, in addition to decreasing friction, the lubricant can act as a heat insulator, limiting the transfer of heat away from the worm and worm gear wheel. These attempts have concentrated on solving the excessive heat build up and wear of the gears by reducing friction. All of these attempted solutions reduce friction and lessen the contact between the worm gear and the drive gear wheel. So when the motor is stopped and the load is in the desired place, the system experiences what is called running back, or overrunning, so that the load continues to be lowered beyond its desired position. Several tries are often necessary to finally get the load in its desired position. This is especially a problem when trying to stop the drive during the lowering of the load and can also create safety problems.
For the foregoing reasons, there is a need, therefore, for a drive system that operates on the principle of friction, yet does not experience running back when raising and lowering a load, does not result in warping and bending of components due to excessive temperature generated as a byproduct of friction and does not require excessive lubricating that can limit the transfer of heat away from the components.